Biochar is a carbonized material obtained from the pyrolysis of biomass produced in a limiting environment of zero or very low oxygen. Its interest lies in its versatility for different applications in the water treatment, soil pollution, mitigation of greenhouse gases, etc. The synergy of this product with other amendments such as compost has been studied for different applications in the soil, including environmental remediation, crop yield, etc. The aim of the research is to identify the relevant aspects in the scientific literature of biochar, compost and soil through a bibliometric analysis for which 753 articles were selected from the Scopus database, having as keywords “biochar”, “compost” and “soil”. This research used R software, specifically the package Bibliometrix, to analyze descriptive analysis, author sources, document metrics, citation, co-citation analysis, co-occurrence network, co-word analysis, and collaboration analysis. Results showed that Zhang Z is the author with the greatest number of documents, and with a higher H index. Science of The Total Environment, Bioresource Technology, and Agronomy are the 3 topmost relevant sources. The keywords according to bond strength and most frequent use were biochar (538 occurrences), composting (349 occurrences), compost (436 occurrences), charcoal (295 occurrences), soil (255 occurrences). China is the country with the most collaboration. It is hoped that the bibliometric review will help to identify current research trends and provide information on the application of biochar and compost in the soil.

The co-treatment of acidic water (AW) and urban wastewater (UWW) is a technique that allows mitigating the negative impact of AW on natural aquatic environments, which represents one of the major environmental problems globally. The aim of this research was to determine the optimal conditions through the response surface methodology (RSM) with a central composite design (CCD) for the co-treatment of AW from the Quiulacocha lagoon in Pasco and UWW from a municipality in Lima, Peru, having as factors the molar ratio of total iron (FeT) and total phosphorus (PT), time (min) and stirring speed (rpm). Data processing was performed using the Design-Expert 11 software, and analysis of variance (ANOVA) with a confidence interval of 95% (α = 0.05) was used. The statistical models obtained showed high determination coefficients (R²), higher than 92% for pH, conductivity and FeT removal. While the removal of COD, PT and obtained a value of R²>0.80, as well as evidenced compliance with the level of significance P value > 0.05. The optimal conditions determined by the statistical model were given at a FeT /PT molar ratio (33:1), a stirring time of 5 min and a speed of 255 rpm. In these conditions, the COD was reduced by 71.78%, FeT by 99.48%, and PT by 84.29% with a residual concentration of 1.3 mg/L; the pH obtained a value of 5.7 and the turbidity 56 NTU. Better efficiency of the co-treatment for the reduction of pollutants in the AW of the Quiulacocha lagoon is evidenced, applying an experimental design to optimize the operating conditions, taking into account that the molar ratio is a significant factor and that optimizing it would allow the co-treatment to be replicated. Co-treatment is a sustainable and promising alternative for the treatment of AW and UWW, since it does not require the use of chemical agents to treat water. However, post-treatments would still be required to comply with certain regulations or to reuse the treated water on a larger scale.

This research reports a bibliometric analysis using the bibliometrix package with information from the SCOPUS database. A descriptive analysis was performed to provide an overview of the countries, institutions, authors, journals and keywords of 80 manuscripts published between 1997 and 2022 in the field of study of emergy and its application in wastewater treatment. The results showed 2 sources with the highest h and g impact index (Ecological Engineering and Journal of Cleaner Production) with a significant growth since 2009. The most cited keywords were "emergy" and "wastewater", and the countries with the most important scientific networks were China, Japan, Saudi Arabia, USA, Brazil, Colombia and Italy. In addition, it shows that collaborative groups among the authors from China and USA are the ones that consolidate the main research network, as well as the largest scientific production with the most cited articles in the field of study of emergy in wastewater treatment. Therefore, the application of the emergy method in wastewater treatment requires extensive research in different types of treatments. This type of analysis would allow the development of a new approach in the application of wastewater treatment in terms of sustainability and the introduction of Latin American countries in this emerging field.

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